I assumed "replace ABC" meant I was being offered the chance to replace an archived copy of the tune on the site somewhere, so not wanting to overwrite somebody else's work, I didn't dare use it. "Display transposed ABC" would be clearer.

Virtually none of the strathspeys already on the web will have that %%MIDI line. Transcribers can't be expected to anticipate bizarre implementations like that when the standard says quite clearly that 3:1 is meant. (The default for abcmidi is 2:1, and does *not* need to be set - if you got a warning that you needed to set the ratio every time you used a broken-rhythm construct it wouldn't be quite so bad).